Magnetically actuated and restored print hammer

ABSTRACT

A magnetic actuator comprises a three-legged magnetic core with an armature pivotally mounted at the middle leg to have portions on either side thereof with an abutting gap relation with one outer leg and an abutting plus a peripheral gap relation with the other. A winding on the one abutting leg provides drive flux, and a winding or permanent magnet on the other leg provides a restore or detent flux between teeth on the armature and core.

United States Patent 7 v Field of Search.....l0l/93 C; 335/229, 230, 279,

[151 3,705,370 Chai et al. 1 Dec. 5, 1972 [54] MAGNETICALLY ACTUATED AND [56] References Cited RESTORE!) PRINT HAMMER UNITED T S PATENTS [72] Inventors: Hi D. Chai, Vestal; Stephen H. R24 209 9/1956 Bernstein 335/274 X Mills, Newark Valley; Joseph P. 1 Pawletko; FrancisE. Petersboth of 2,827,529 3/1958 DeQFlrgue ..335/276X gz z g g Young Bmgham' Primary Examiner-George Harris Attorney-Hanifin and Jancin and Francis V. Giolma [73] Assignee: International Business Machines Corporation, Armonk, N.Y. [57] ABSTRACT [22] Filed: April 1971' A magnetic actuator comprises a three-legged mag- [21] Appl 134,176 netic core with an armature pivotally mounted at the middle leg to have portions on either side thereof with i an abutting gap relation with one outer leg and an {2% 8''. 335/229 3 8 abutting plus a peripheral gap relation with the other. [58% n A winding on the one abutting leg provides drive flux and a winding or permanent magnet on the other leg provides a restore or detent flux between teeth on the armature and core.

5 Claims, 4 Drawing Figures c2 I43 I --g2 it E?" 720 74 it Q e 56 g5 66 54 TORQUE PATENTEDBEI: 5 I972 RESULTANT T1 & TG2" 7 ROTATION FIG. 4

INVENTORS HI D. CHAT STEPHEN H. MILLS JOSEPH P. PAWLETKO FRANCIS E. PETERS BY CARL T. YOUNG QM 'llfjpr nw ATTORNEY MAGNETICALLY ACTUA'IED AND RESTORED PRINT HAMMER CROSS-REFERENCE To RELATED APPLICATION This invention is related to the invention of co-pending application, Ser. No. 134,254, of Joseph P. Pawletko, Francis E. Peters, Carl T. Young and John E. Kroft,

filed Apr. 15, 1971. H

FIELD OF INVENTION DESCRIPTION OFTHE PRIOR ART Print hammer structureshave. heretofore comprised separate hammer members mechanically coupled to amagnetic actuator or the like by pushrods as in the James M. Cunningham US. Pat. No. 3,241,480, which issued on Mar. 22, 1966. 1

(SUMMARY OF THE INVENTION Generally stated, it is an object of this invention to provide anewand novel magnetic actuator.

More specifically, it is an object of this invention to provide a magnetically operated print hammer with improved performance.

Another object of the invention is to provide an electromagnetically operated print hammer having a single movable element.

Yet another object of the invention is improving the settle-out time of a operated print hammer.

' It is also an object of the present invention to provide a magnetically operated print hammer having an inverse squar e law operating characteristic and a modified restoremagnetic characteristic.

Another object of this invention is to provide for combining a variabl e reluctance constant length air gap with a variable length variable reluctance air gap in the restore magnetic circuit of an electromagnetically operated print hammerin order to improve the restore characteristics of the print hammer.

Yet another important object of this invention is to provide for reducing the restore time of an electromagnetically operated print hammer and also reduce the likelihood of rebound upon restoration to the. nonoperated position.

The foregoing and other objects, features, and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention as illustrated in the accompanying drawing.

DESCRIPTION OF THE DRAWING In the drawing: 7

FIG. 1 is a schematic view in side elevation of a magnetically operated print hammer embodying the invention in one form;

FIG. 2 is a schematic view in side elevation of a magnetically operated print hammer embodying the invention in a different form; I 1 1 FIG. 3 is a chart showing torques acting on the armature of the actuator for different positions of the arma ture; and e to provide for magnetically FIG. 4 is a schematic equivalent magnetic circuit diagram for the print hammer of FIG. 2.

DESCRIPTION OF PREFERRED EMBODIMENTS has a cylindrical Surface Portion 16 which cooperates with a corresponding cylindrical Surface Portion 17 of an Armature 18, which is typically mounted at or adjacent the Middle Leg 14 by means of a Pivot Shaft 20, and has an upwardly-extending Arm or Actuator Portion 22, shown disposed in predetermined'spaced relation with the end of the Upper Leg 13 to-defme an air gap G2. At the upper end the. Extension 22 is provided witha Hammer Face 24 for impacting a Document 26 and a Ribbon 28 against a Type Member 30, which may be mounted on a belt or the like (not shown) for movement past a print position. The lower end of the Armature 18 may be provided with a hooked portion providing a Pole Piece 32, which cooperates with the Lower Leg 15 and is shown in substantially abutting relation therewith.

The Upper Leg 13 of the Core Member 12 may be provided with a winding or the like for providing a detent flux or, as shown, may comprise a Permanent Magnet 11 to supply magnetic flux for normally attracting the Armature 18 to a rest position in abutting relation therewith. An Operating Winding 34 is provided on the Lower or Drive Leg 15 and, as shown, is positioned to surround the end portion of the Pole Piece 32 of the Armature 18 so that the air gap G1 between the lower end of the armature 18 and the Lower Leg 15 will be within the confines of the Winding 34. The'Middle Leg 14 in addition to having the cylindrical Surface Portion 16, has an adjoining relatively flat radial Pole Face or Surface Portion 40, which cooperates with a corresponding relatively flat radial Pole Face or Surface Portion 42, on the Armature 18 to provide abutting Pole Faces.

The Armature 18 will normally be held in abutting .relation with the Upper Leg 13 because of magnetic flux produced by the Permanent Magnet 11, which follows a path through the Upper and Middle Legs-l3, 14 and the intermediate portion of the Armature 18. When the Winding 34 is pulsed, sufficient magnetic flux is produced between the Lower Leg l5 and the Lower-End 32 of the Armature 18 to overcome the holding effect of the Permanent Magnet 11, causing the Armature 18 to rotate in a clockwise direction, closing the gap G1 and causing the Hammer Face 24 to impact the Paper 26 and Ribbon 28 against the Type 30 for printing. When the pulse applied to the Winding 34 is terminated, the magnetic flux produced by the Permanent Magnet 1 l is sufficient to restore the Armature 18 to the non-operated position against the end of the Permanent Magnet 11.

In this embodiment additional working forces are added, to increase the acceleration rate of the Armature 18 because of-the added tangential forces between the Pole Faces 40 and 42 adjacent the Operating Winding 34. Better cancellation of the DO. field occurs with this magnetic arrangement, and the restore characteristic is better because less D.C. flux leaks through the drive pole path across air gap G1. In addition, lower bearing forces are experienced during the drive cycle, since most of the forces are tangential rather than radial.

Referring to FIG. 2, it will be seen that the reference numeral 41 designatesa generally similar Electromagnetic Actuator comprising a three-legged magnetic Core 44 having Upper, Middle and Lower Leg Portions 46, 48 and 50, and an Armature 52 pivotally mounted by means of a Pivot 54 opposite a cylindrical End Portion 56 of the Middle Leg 48, much the same as described in connection with the actuator of FIG. 1. The Armature 52 likewise has an upstanding Arm or Actuator Portion 58, which carries at its upper end a Hammer Face 60.for impacting a document, ribbon and type as described in connection with the actuator of FIG. 1. Likewise, the Armature 52 is provided with a hooked End Portion 62 at the lower end, which defines with the Lower Leg Portion 50 a substantially radial air gap G1 located within the confines of an Operating Winding 64. As described in connection with the actuator of FIG. 1, an adjoining substantially flat radial Pole Face 66'is provided adjacent the cylindrical end of Fortion 56 of the Middle Leg 48 and a corresponding Pole Face 68 is providedon the Armature 52.

The Upper Leg Portion of the Electromagnetic Core 44 may comprise a' Permanent Magnet 43 as was the case in connection with the actuator of FIG. 1. A Pole Piece 70 is provided at the end of the permanent magnet. The Pole Piece 70 has a Pole Face 71 defining with the Armature 52 the air gap G2. In addition, the Pole Piece 70 has a curved peripheral Face 72 definedv by a plurality of spaced Teeth 72a 72d. The Armature 52 is provided with a corresponding peripheral curved Portion 74 having a similar arrangement of spaced Teeth 74a 74d. These teeth, when the armature is in the operated position, as shown, are substantially displaced and overlap onthe order of -40 percent. In the normal or non-operated position, when the flux from thePermanent Magnet 43 attracts the Armature 52 into abutting relation withthe Pole Piece 70, the Teeth 72a 72d, and 74a 74d will be substantially in alignment.

-With the Armature 52 in abutting relation with the Pole Face 71,.energization of the Operating Winding 64 produces a magnetic flux in the Lower Leg Portion 50, which results in a torque sufficient to overcome the restore torque of the permanent magnet so that rotation begins. The Armature 52 rotates in a clockwise direction until impact against the document occurs.

The steady-state magnetic flux produced by the Permanent Magnet 43 effects the restore of the Armature 52 in a counterclockwise direction as soon as the energization ofth e Operating Winding 64 is terminated. The effects of the parabolic torque characteristic of the Teeth 72a 72d, and 74a 74d and the square law characteristic of the radial or abutting gaps may be seen by reference to the curves T01, T63 and TG2 and Tr of FIG. 3, which show respectively the torques on the armature, namely, the torque of the Pole Face G1, plus G3, the torque of Pole Face G2, and the torque of the restore Teeth 72a 72d, and 74a 74d.

In order to explain the principle of operation of this actuator it is convenient to use an equivalent circuit shown in FIG. 4. Notations in the equivalent circuit signify the following:

F1, F2 Magnetomotive forces of the Guide Winding 64 and the Permanent Magnet 46, respectively.

411, 42, and (1:3 Fluxes in the lower, upper and middle legs, respectively.

R1, R2, and R3 Reluctances between the points P and Q to the lower, upper and middle legs, respectively.

R2 is given by:

where Rm is the magnet and iron reluctance and R! and Rg2 are the reluctance between flat pole faces and the reluctance between the stator and armature teeth, respectively.

R3=R3+RcX(Rg3/Rc-l-Rg3) (la) where R3 is the iron reluctance in the middle leg between P and Q; Re is the reluctance of the fixed circular gap, and R33 is the reluctance of the flat pole face.

where A= RlR2+R2R3+R1R3 The torque on the armature is T= Tgl+Tg2+Tg3+Tt (4) where Tgl, Tg2, Tg3, T: are the torques at the lower pole face, upper pole face, middle pole face, and teeth, respectively. They are given by:

where:

A l A2, A3 Effective cross-sectional areas of lower, upper and middle stator pole faces, respectively.

ll, [2, I3 Effective moment arms of lower, upper and middle stator pole faces, respectively.

Tt=+k tsin00 sOs 0 8 Equation (8) results from the assumption that the teeth gap reluctance varies sinusoidally, and the torque on the armature in the counterclockwise direction is positive. k is a constant to be determined for the assumed reluctance variation.

Before-the drive pulse is applied, F1 is zero, (#2 is larger than (111, and the torque is positive. These conditions imply that the armature is at the backstop. When a voltage is applied at the drive coil, or and g3 increases, the torque becomes negative, and the armature starts to move in the clockwise direction.

Two things should be noted here. First, R3 is much smaller than R2, and very little flux derived from the drive pulse goes through the upper leg. Consequently, the drive pulses contribution to the counterclockwise torque is negligible. Secondly, the initial flux at the drive leg is non-zero. Since the rate of change of the drive torque (Tgl) is proportional to bl and dl/dt, a faster buildup of the torque is expected than in a situation where (#1 is zero.

The drive current is applied to the actuator until the desired impact energy is developed. It is then removed so that the current is zero at the time of impact. At impact, the reluctance torque (T!) is large, and this in turn causes the armature to restore faster and reduces the time the print head is in contact with the paper. As

the armature returns to the backstop after the impact, I

4:32 increases. As a result, Tg2, which serves to impede the rebound at the backstop, increases while Tt decreases.

Energy in the armature is also absorbed by a highly absorptive residual which is positioned on the backstop. The rebound effect can be further reduced by pulsing the drive coil in the return cycle to minimize the kinetic energy of the system.

In one embodiment'of the actuator, as shown in FIG. 2, typical data is as follows:

Impact Energy 35-65K ergs Impact Velocity 78-105 in/sec Hammer Stroke ().035-0.055 in Flight Time l.352 millisec Repetition Rate 3-5 millisec Drive Voltage 24-48 Volts Current 2.5-4 Amp Drive Pulse Width O.85l.l millisec Efficiency 4.2-7.5 percent Contact Time 30-100 Usec While the invention has been shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. In an electromagnetic actuator,

having a cylindrical surface portion at the end of the middle leg,

a three-legged magnetic core member having a cylindrical surface portion at the end of the middle leg, an. armature of magnetic material having a pivotal support adjacent the middle leg of said core member with a corresponding cylindrical surface portion concentric with said pivotal support and positioned in close relation with the cylindrical surface portion of said middle leg to provide a constant reluctance pin gap, said armature having portions extending on opposite sides of said pivotal support point positioned in spaced relation with the ends of the outer legs'of said core member with one of said portions extending beyond the end of one of said outer legs to provide an actuating arm, means for producing a restore magnetic flux in said one outer leg to hold said armature against the end of said one outer leg, and I an operating winding positioned on said other outer leg disposed to be energized to overcome the effects of the means producing said restore magnetic flux, whereby the armature is actuated to separate said armature from said one associated outer leg of said core member and operate said arm. 2. The invention as defined in claim 1 characterized by said armature having a peripheral curved surface portion defined by a plurality of spaced tooth portions adjacent said one outer leg, and said one outer leg having corresponding tooth portions which are displaced peripherally of the armature tooth portions when the armature is rotated awajy from said outer l 3. The invention as e fined in claim 2 gfiaracterized by said middle leg and said other outer leg being separated by a narrow slotwhich receives a portion of said operating winding.

4. The invention as defined in claim 3 characterized by said middle leg having a substantially radially disposed flat pole face adjacent said cylindrical surface portion on the side of said pivotal support adjacent said other outer leg and said armature having a corresponding pole face disposed to abut therewith in the operated position.

5. The invention as defined in claim 1 characterized by said one leg comprising a permanent magnet having a pole piece with adjacent abutting and toothed peripheral pole faces. 

1. In an electromagnetic actuator, having a cylindrical surface portion at the end of the middle leg, a three-legged magnetic core member having a cylindrical surface portion at the end of the middle leg, an armature of magnetic material having a pivotal support adjacent the middle leg of said core member with a corresponding cylindrical surface portion concentric with said pivotal support and positioned in close relation with the cylindrical surface portion of said middle leg to provide a constant reluctance pin gap, said armature having portions extending on opposite sides of said pivotal support point positioned in spaced relation with the ends of the outer legs of said core member with one of said portions extending beyond the end of one of said outer legs to provide an actuating arm, means for producing a restore magnetic flux in said one outer leg to hold said armature against the end of said one outer leg, and an operating winding positioned on said other outer leg disposed to be energized to overcome the effects of the means producing said restore magnetic flux, whereby the armature is actuated to separate said armature from said one associated outer leg of said core member and operate said arm.
 2. The invention as defined in claim 1 characterized by said armature having a peripheral curved surface portion defined by a plurality of spaced tooth portions adjacent said one outer leg, and said one outer leg having corresponding tooth portions which are displaced peripherally of the armature tooth portions when the armature is rotated away from said outer leg.
 3. The invention as defined in claim 2 characterized by said middle leg and said other outer leg being separated by a narrow slot which receives a portion of said operating winding.
 4. The invention as defined in claim 3 characterized by said middle leg having a substantially radially disposed flat pole face adjacent said cylindrical surface portion on the side of said pivotal support adjacent said other outer leg and said armature having a corresponding pole face disposed to abut therewith in the operated position.
 5. The invention as defined in claim 1 characterized by said one leg comprising a permanent magnet having a pole piece with adjacent abutting and toothed peripheral pole faces. 